1. Field of the Invention
The present invention relates to methods of manufacturing golf club heads which have formed therein hollow sections and which are made of titanium or an alloy thereof and, more particularly, to a method of manufacturing a golf club head made of titanium or an alloy thereof, referred to as "metal wood".
2. Prior art
Conventionally, a head for a driver or the like in golf clubs is made of wood. The golf club generally has a metallic plate mounted to a sole face of the wood head, and an insert made of a resinous material or the like is mounted to a face of the head to reinforce the latter. In recent years, however, drivers and other golf clubs have appeared which have heads made of metal or an alloy thereof, called "metal wood". A golf club having a head made of metal or alloy thereof will hereinafter be referred to as "metal wood". Golfing using a metal wood lengthens the distance a hit ball will fly, improves aim accuracy, and generally facilitates hitting the ball. Thus, metal wood heads have been replacing wood heads in golf clubs such as drivers or the like.
Particularly, in recent years, it has been proposed to form a metal wood out of titanium or an alloy thereof which is superior in repulsion force and corrosion resistance and which is light in weight, as disclosed in, for example, Japanese Patent Provisional Publication No. SHO 63-154186. The head made of titanium or alloy thereof is manufactured in the following manner. That is, as shown in FIG. 6 of the attached drawings, the titanium or alloy thereof is pressed by a press machine to manufacture a face shell piece 111, an upper-face shell piece 112 and a sole-face shell piece 113. A balance weight 114 is mounted to an inner surface of the sole-face shell piece 113. Subsequently, the plurality of shell pieces 111, 112 and 113 are united together by means of welding. In this manner, the metal wood head is manufactured.
However, the following problems arise. That is, considerable skill is required to weld the plurality of pressed shell pieces in a clean or beautiful manner. Further, weld beads produced by the welding must be ground and polished so that surfaces of the weld beads are smoothed. Accordingly, the greater the length of the welds, the higher manufacturing costs.
Moreover, the following problems also arise. That is, if a plurality of pressed shell pieces having respective forged structures are welded together, strain remains at the welded or joined sections because the forged structures of the respective shell pieces are different from the welding structure of the weld beads. The longer the welding joined sections, the more the residual strain. Furthermore, if minute or fine weld defects such as pinholes or the like exist in the welding joined sections, cracks develop at the welding joined sections. Thus, it is impossible to adequately utilize the superior repulsion force of the titanium or alloy thereof.
The inventors of the present application have conducted research directed toward the manufacture of a head for a metal wood, which is low in manufacturing cost and which has fewer weld defects and less residual strain. As a result, the inventors have discovered the following.
A major part of the head, which has a small opening and a hollow section and which is made of titanium or an alloy thereof, is manufactured by precision casting. Then, a balance weight is inserted into the hollow section through the opening and is fixedly mounted to the head. Subsequently, the opening is closed, in a sealed manner, by a closure which is manufactured by pressing and which is made of titanium or an alloy thereof. The head thus produced has the following advantages. That is, since the weld bead for sealing the small opening is shortened, there is a reduction in weld defects and residual strain. Further, post-treatment after welding, such as grinding and polishing of the weld bead, is reduced. Thus, the manufacturing cost can be reduced considerably. Moreover, it is possible to sufficiently exhibit the repulsion force of the titanium or alloy thereof.